Engineering the band gap of bare titanium dioxide materials for visible-light activity: a theoretical prediction

The main obstacle for the practical application of common titanium dioxide (TiO2) photocatalysts is that they can only absorb ultraviolet sunlight. Fluorite TiO2 has attracted considerable interest since it may utilize more abundant visible sunlight. However, its electronic properties have not yet been confirmed according to the previous theoretical investigations. In this study, density functional theory with different exchange-correlation functionals was employed to explore the electronic structure of fluorite TiO2 materials. Our results demonstrate that the perfect fluorite TiO2 crystals are indirect semiconductors. The size of supercells plays an important role for the calculation outcomes due to the Brillouin zone folding. The theoretical band gap energy of fluorite TiO2 using the hybrid DFT method is 2.31 eV, which supports its photocatalytic activity with visible light. The surrounding static electric fields of Ti cations of fluorite TiO2 are responsible for the reduced bang gap energies on the basis of crystal field theory. According to our theoretical deduction, possible visible-light responsive TiO2 photocatalysts were proposed by tuning the atomic configurations of the rutile TiO2 (110) surface.